Megger DET3TA Manuale utente

DET3TA, DET3TC, DET3TD and DET4TD

Earth Ground Electrode Testers

USER MANUAL

GSAFETY WARNINGS

■Safety Warnings and Precautions must be read and understood before the instrument is used. They must be observed during use.

■Do not leave the instrument connected to the system under test when not in use.

■Circuit connections and exposed metalwork of an installation or equipment under test must not be touched.

■The instrument must not be operated or connected to any external system if it shows any visible signs of damage or if it has been stored for prolonged

periods in unfavourable conditions.

■The instrument must not be operated or connected to any external system if the battery compartment or casing is open or any parts of the case

(including keypad, selector switch, display window, etc.) are missing.

■The earth spikes, test leads and their terminations (including connections to the earthing system under test) must not be touched if an installation earth

fault can arise unless adequate precautions are taken.

■The earth spikes, test leads and their terminations (including connections to the earthing system under test) must not be touched while the instrument

is switched on.

■Special precautions are necessary when operating in situations where ‘live’ earths may be encountered: isolation switches and fuses (not supplied with

this instrument) must be used.

■Special precautions are necessary when working near high tension systems (MV and HV): rubber gloves and shoes (not supplied with this instrument)

should be worn.

■Special precautions are necessary when working in wet conditions or in agricultural areas: observe the local safety standards and take all necessary

special precautions applicable to the particular location.

■The instrument must be disconnected from the earthing system under test while batteries are being changed or the fuse replaced.

■Replacement batteries and fuses must be of the correct type and rating.

Users of this equipment and/or their employers are reminded that National Health and Safety Legislation requires them to carry out valid risk assessments of

all electrical work so as to identify potential sources of electrical danger and risk of electrical injury such as inadvertent short circuits. Where the assessments

show that the risk is significant then the use of fused test leads may be appropriate.

NOTE

THE INSTRUMENT MUST ONLY BE USED BY SUITABLY TRAINED AND COMPETENT PERSONS.

GLIVE EARTH SAFETY PRECAUTIONS

It is preferable that the earth electrode to be tested is first isolated from the circuit it is protecting, so that only the earth is measured and not the complete

system. When this is done, the circuits and equipment must be de-energised. If however this is not possible, the earth electrode should be duplicated so that

when it is disconnected for test purposes, the other one provides the necessary circuit protection. The following safety precautions are essential when

working near high tension systems where any unintentional ‘live’ earths may be encountered between the site earth and remote earths established for test

purposes. A ‘live’ earth is one that carries current from the mains supply, or could do so under fault conditions.

1. All persons involved must be trained and competent in isolation and safety procedures for the system to be worked on. They must be clearly instructed

not to touch the earth electrode, test spikes, test leads, or their terminations if any ‘live’ earths may be encountered. It is recommended that they wear

appropriate rubber gloves, rubber soled shoes, and stand on a rubber mat.

2. The ‘P’ (‘S’) and ‘C’ (‘H’) terminals should be connected through a double pole isolation switch, the rating of which will cope with the maximum fault

voltage and current. The isolation switch must be open whilst any personal contact is made with the remote test spikes, or the connecting leads, e.g.

when changing their position.

Note: If a fault occurs while a test is being made the instrument may be damaged. Incorporating fuses at the isolation switch, rated at 100 mA, and able to

cope with the maximum fault voltage will provide some protection for the instrument.

BATTERY INSTALLATION

Caution: Whenever battery cells are being fitted or replaced, there should be no connections to the instrument terminals. The cover to the battery

compartment lifts off the rear of the instrument and is held in position by a single captive screw in the base of the instrument. To fit or replace battery cells,

loosen the captive screw and lift away the cover. Fit new cells observing the correct polarity as indicated on the battery compartment moulding. Replace the

cover and tighten the securing screw. To avoid damage by leaking electrolyte, do not leave cells fitted in an instrument which will remain unused for

extended periods of time.

Symbols used on the instrument are:

GCaution: refer to accompanying notes

tEquipment protected throughout by Double

Insulation (Class II)

cEquipment complies with current EU directives.

Equipment complies with ‘C tick’ requirements

CONTENTS

Safety notices 2

Introduction 5

General description 5

Instrument illustrations 6

Preparations for use (all instruments) 8

General operating instructions (all instruments) 9

Replacing batteries and fuses 10

Megger’s ‘Down to Earth’ publication 11

Description of Tests for Models DET3TD, DET3TC and DET4TD 11

Battery 11

Measurement of ground noise voltage 11

Two-terminal resistance measurement 12

Three-terminal ground rod resistance measurement 12

Four-terminal ground rod resistance

measurement (DET4TD) 13

Ground resistance measurement (DET4TD) 13

Calibrating the instrument to the ICLAMP (DET3TC) 14

Measuring ground current with the ICLAMP (DET3TC) 14

Measuring ground resistance with the ICLAMP (DET3TC) 14

Attached Rod Technique (ART) (DET3TC) 15

Measuring ground resistance with the ICLAMP using the

ART (DET3TC) 15

Description of Tests for Model DET3TA 16

Battery-life reading 16

Ground noise voltage measurement 16

Two-terminal resistance measurement 17

Three-terminal resistance measurement 17

Preventative instrument maintenance 19

Technical specifications 19

Repair and Warranty 21

N1311

The Megger DET family of test instruments offers a unique solution to the

measurement of earth or ground electrode (rod) resistance and soil

resistivity. The family has three digital variants, which support 2, 3 and 4

point (DET4TD only) testing, and one analogue version that makes

provision for 2 and 3 point measurements.

The DET3TC can use an optional current clamp (ICLAMP) to measure

electrode (rod) resistance without disconnection, leaving the installation

earthing system intact (Attached Rod Technique, ART). The DET3TC in

conjunction with the current clamp can also measure conductor current.

The DET variants have the following features:

Feature DET3TA DET3TC DET3TD DET4TD

Automatic C spike check ■■ ■

Automatic P spike check ■■ ■

Manual P spike check ■

Automatic noise check ■■ ■

Manual noise check ■

Noise rejection (40 V pk-pk) ■■■ ■

2-wire test ■■■ ■

3-wire test ■■■ ■

4-wire test ■

No disconnect testing (ART) ■

Voltmeter (ground noise

voltage measurement) ■■■ ■

INTRODUCTION GENERAL DESCRIPTION

Thank you for purchasing the Megger Earth Ground Electrode Tester.

For your own safety and to get the maximum benefit from your

instrument, please ensure that you read and understand the following

safety warnings and instructions before attempting to use the instruments.

This user manual describes the operation and functions of the DET series

of Earth Ground Electrode Testers:

DET3TA

DET3TC

DET3TD

DET4TD

DET3TA

INSTRUMENT ILLUSTRATIONS

Feature DET3TA DET3TC DET3TD DET4TD

Current measurement ■

LCD display ■■■

Moving coil meter ■

IP54 rated ■■■ ■

EN61010-1 100 V CATIV ■■■ ■

Each instrument kit comprises instrument, test leads, test spikes, batteries

and calibration certificate stored in a tough polypropylene carrying-case.

Test lead connections

(at rear)

Rc OK

Selector switch

Resistance

measurement

settings (2P and

3P)

Resistance scale

Voltage scale

Potential test spike

resistance indicator

Battery charge indicator

Test lead connections (at rear of instrument)

Battery check setting and

voltage setting

Multi-function

analogue display

Test button

P Spike button

DET3TC DET3TD

Test lead connections

(at rear)

Resistance

measurement settings

(2P, 3P and clamp)

Selector switch

Voltage and current

measurement settings

Test button

Digital LCD display Digital LCD display

Warning - refer to

User manual Battery charge

indicator

Measuring range Measuring range

Ruptured fuse

indicator

Over/under range

indicator

Potential probe

resistance indicator

(OK or high) Current probe resistance

(OK or high)

Clamp current indicator

(OK or low)

Ground noise voltage

indicator (OK high)

Test lead connections (at rear of instrument) Test lead connections (at rear of instrument)

Warning - refer to

User manual

Over/under range

indicator

Ruptured fuse

indicator

Potential probe

resistance indicator

(OK or high) Current probe resistance

(OK or high)

Ground noise voltage

indicator (OK high)

Battery charge

indicator

Test lead connections

(at rear)

Resistance

measurement settings

(2P and 3P)

Selector switch

Voltage measurement

settings

Test button

Batteries

The Megger DET series instruments are supplied with batteries fitted.

When batteries become exhausted, refer to the section on battery

replacement.

Warning: Do not switch the instrument on with the battery cover

removed.

Inspection

Before each use of the instrument, visually inspect the instrument case,

test leads, spikes and connectors to confirm that their condition is good,

with no damaged or broken insulation.

DET4D

PREPARATIONS FOR USE (ALL INSTRUMENTS)

Test lead connections (at

rear of instrument)

Resistance measurement

settings (2P, 3P and 4P)

Selector switch

Voltage

measurement

settings

Test button

Warning - refer to

user manual

Ruptured fuse

indicator

Under/over

range indicator

Potential probe

resistance (OK or

high)

Test lead connection (at rear of instrument)

Current probe

resistance indicator

(OK or high)

Ground noise voltage

indicator (OK or high)

Measurement ranges

Battery charger

indicator

Digital LCD display

Instrument output voltage selection

The maximum output voltage of the instrument is nominally 50 V. Should

it prove necessary in particular circumstances, it is possible to set the

output voltage 25 V. The procedure for changing the output voltage is as

follows:

1. Press and hold the TEST button and switch instrument ON to the V

setting on the selector switch.

2. The LCD display will indicate ‘tst’ (DET3TC, DET3TD and DET4TD).

3. Release TEST button. The maximum output test voltage will be

displayed, either ‘50 V’ or ‘25 V’.

4. To toggle between the maximum output test voltages, press the TEST

button.

5. Switch off instrument when the desired maximum test voltage is

displayed.

Auto power down

To extend battery life the instrument will automatically switch off six

minutes after the last operation.

The instrument can be switched off manually by selecting the ‘OFF’ setting

on the selector switch and then switched on as normal.

Display symbols (DET3TC, DET3TD, DET4TD)

GWarning Triangle

fFuse Blown

Battery Indicator (not DET3TA).

>100V Indicates that the ground noise voltage exceeds the instrument

measurement capability.

Rp OK Potential spike (P Spike) is within range for accurate

measurement (<100 kΩ).

Rp Hi Potential spike (P Spike) resistance exceeds range for accurate

measurement (>100 kΩ).

Rc OK Current spike (C Spike) is within range for accurate

measurement (<100 kΩ).

Rc Hi Current spike (C Spike) resistance exceeds range for accurate

measurement (>100 kΩ).

Noise OK Ground noise voltage is within range for accurate measurement

(<40 Vpk-pk).

Noise Hi Ground noise voltage exceeds range for accurate measurement

(>40 Vpk-pk).

Display symbols (DET3TA)

Current spike (C Spike) is within range for accurate

measurement (<100 kΩ).

Instrument is performing measurement checks.

Note:

Rc and Rp limit reduced to 50 kΩfor 25 V output.

Rc and Rp limit reduced to 5 kΩon 18 Ωrange to achieve 0.01 Ω

resolution.

GENERAL OPERATING INSTRUCTIONS (ALL INSTRUMENTS)

Batteries

Battery type: 8 x LR6 (AA), 1.5 V Alkaline, or 8 x 1.2 V NiCAD, or 8 x

1.2V NiMH

The battery condition is continuously displayed by the bar-graph type

symbol (DET3TC, DET3TD and DET4TD) or by switching to the battery

setting and pressing the TEST button (DET3TA).

Figure 1 shows the progression of the battery indicator (for the DET3TC,

DET3TD and DET4TD) which gives a qualitative status of the battery charge

condition.

Fully charged battery

75% charged battery

50% charged battery

25% charged battery

Some testing still possible but battery may fail at any

time

Symbol flashes when there is not enough charge to

do a test and the instrument will turn itself off

Figure 1: Battery life indication (DET3TC, DET3TD, DET4TD)

REPLACING BATTERIES AND FUSES

Note: Fully charged NiMH or NiCAD rechargeable batteries show a lower

charge than alkaline batteries, and may not give much warning before

becoming exhausted

To replace batteries

Warning: Do not operate instrument with the battery cover removed.

1. To avoid the possibility of electric shock, switch instrument ‘OFF’ and

disconnect the instrument from any electrical circuits.

2. The rear cover must not be opened if the test leads are connected.

3. To avoid the possibility of electric shock, do not press the test button or

touch the fuse when changing batteries.

4. To remove the rear cover, release the screw at the bottom of the cover

and lift the cover upwards.

5. Remove the dead cells.

6. Refit new batteries observing the correct polarity as marked on the

battery compartment.

7. Replace the instrument back cover and secure by tightening the

retaining screw.

Warning: - Incorrect battery cell polarity can cause electrolyte leakage,

resulting in damage to the instrument. If the battery condition indicator

does not show a full charge when battery cells are new, a cell may be

reversed.

Note: Battery cells should not be left in an instrument that may remain

unused for extended periods.

Fuse

Fuse type: 500 mA (F), HBC, 50 kA, 600 V (32 x 6 mm)

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